Air filters, such as those used in air cleaner assemblies which filter particulate matter out of an air stream prior to its introduction into the combustion chamber of a vehicle's internal combustion engine, periodically clog and need to be replaced. Such air filters have historically been monitored in an indirect manner to determine when they should be replaced. For example, the number of miles driven by a vehicle since its last air filter replacement is commonly used as a means for determining when it is time to replace a vehicle's air filter. Using miles driven as a basis for making this determination relies on a correlation between the miles driven by the vehicle and the rate at which the vehicle's air filter clogs with particulates.
Although such a method of determining when to replace a vehicle's air filter is adequate, there is room for improvement. This is because the correlation between miles driven by a vehicle and the clogged state of the vehicle's air filter can be affected by the type of environment in which the vehicle is driven. For example, the air filter of a vehicle that is routinely driven through a desert environment will clog at a rate that differs from a vehicle that is routinely driven through an arctic environment because of the difference between the amount of particulate matter suspended in the air of each environment. This difference between environments, as well as other factors, can vary the correlation between the miles driven and the condition of a vehicle's air filter. This, in turn, can diminish the effectiveness of using miles driven as a predictor of when a vehicle's air filter needs to be replaced.
Furthermore, hybrid electric vehicles, plug-in hybrid electric vehicles, extended range electric vehicles, and vehicles operated using other non-traditional power sources, are being introduced into the marketplace. Such vehicles may, at various times and/or for unpredictable periods of time, be powered exclusively by their electric motors. During periods of time when their internal combustion engines are not utilized, the air filters on these new types of vehicles will not clog with particulate matter. Accordingly, the number of miles driven by these vehicles may not be an acceptable means of predicting the condition of their air filters.